Method and device for treating the exhaust gas of an internal combustion engine

ABSTRACT

A device for treating exhaust gas of an internal combustion engine includes a reducing agent solution evaporator, a hydrolysis catalytic converter connected thereto for hydrolysis of urea to form ammonia and an SCR catalytic converter for selective catalytic reduction of nitrogen oxides. The evaporator includes an evaporator unit providing a gaseous substance mixture including at least one reducing agent precursor and/or reducing agent. The evaporator unit evaporates an aqueous solution including at least one reducing agent precursor. The SCR catalytic converter is in an exhaust line, and the evaporator and the hydrolysis catalytic converter are outside of and can be connected to the exhaust line. A sufficiently large quantity of reducing agent for selective catalytic reduction of nitrogen oxides in the SCR catalytic converter can be provided, while permitting a smaller volume of the hydrolysis catalytic converter than in the prior art, since it is not traversed by exhaust gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuing application, under 35 U.S.C. § 120, of copendingInternational Application No. PCT/EP2007/004359, filed May 16, 2007,which designated the United States; this application also claims thepriority, under 35 U.S.C. § 119, of German Patent Application DE 10 2006023 145.7, filed May 16, 2006; the prior applications are herewithincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method and a device for treating theexhaust gas of an internal combustion engine, in which the content ofnitrogen oxides in the exhaust gas of the internal combustion engine isreduced through selective catalytic reduction.

The emission into the environment of substances contained in the exhaustgas from internal combustion engines, is undesirable. In many countries,for example, nitrogen oxides (NO_(X)) may only be contained in theexhaust gas of internal combustion engines up to a certain limit value.In addition to engine-internal measures, through the use of which theemissions of nitrogen oxides can be reduced by a selection of a suitableoperating point of the internal combustion engine, aftertreatmentmethods have been established which make a further reduction of thenitrogen oxide emissions possible.

One option for further reducing the nitrogen oxide emissions isso-called selective catalytic reduction (SCR). In that case, a selectivereduction of the nitrogen oxides to form molecular nitrogen (N₂) takesplace by using a selectively acting reducing agent. One possiblereducing agent is ammonia (NH₃). In that case, ammonia is often storednot in the form of ammonia but instead, an ammonia precursor is stored,which is converted to ammonia when required. Possible ammonia precursorsare, for example, urea ((NH₂)₂CO), ammonium carbamate, isocyanic acid(HCNO), cyanuric acid and the like.

Urea, in particular, has proven to be simple to store. Urea ispreferably stored in the form of a urea/water solution. Urea and, inparticular, urea/water solution is hygienically harmless, simple todistribute and to store. A urea/water solution of that type is alreadymarketed under the trademark “AdBlue”.

German Published, Non-Prosecuted Patent Application DE 199 13 462 A1discloses a method in which a urea/water solution is dosed, upstream ofa hydrolysis catalytic converter, into a partial flow of the exhaust gasof an internal combustion engine. The dosing-in process takes place inthat case in the form of droplets. When the droplets impinge on thehydrolysis catalytic converter, hydrolysis and thermolysis of the ureatakes place to form ammonia, which is used as a reducing agent in an SCRcatalytic converter situated downstream. The method described thereinhas the disadvantage that the hydrolysis catalytic converter is cooledby the evaporation of the urea/water solution. In particular, wherelarge quantities of ammonia are required, it is thus possible, at leastin regions of the hydrolysis catalytic converter, for such intensecooling to take place that, in that case, the hydrolysis reaction nolonger takes place or no longer takes place completely. Furthermore, asa result of the locally severely discontinuous cooling of the hydrolysiscatalytic converter generated due to the evaporation of the individualdroplets, the hydrolysis catalytic converter can be damaged, and inparticular a catalytically active coating can become detached.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method and adevice for treating the exhaust gas of an internal combustion engine,which overcome or at least alleviate the hereinafore-mentioneddisadvantages of the heretofore-known devices and methods of thisgeneral type.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a device for treating exhaust gas of aninternal combustion engine passing through an exhaust line. The devicecomprises a reducing agent solution evaporator which is disposed outsidethe exhaust line and is to be connected to the exhaust line. Thereducing agent solution evaporator includes an evaporator unitconfigured for evaporating an aqueous solution which includes at leastone reducing agent precursor and configured for providing a gaseoussubstance mixture including at least one of the following substances:

-   -   a) at least one reducing agent precursor, or    -   b) a reducing agent.

A hydrolysis catalytic converter is connected to the reducing agentsolution evaporator for the hydrolysis, in particular, of urea to formammonia, is disposed outside the exhaust line and is to be connected tothe exhaust line. An SCR catalytic converter is disposed in the exhaustline for selective catalytic reduction of nitrogen oxides.

A particulate filter can be provided upstream of the SCR catalyticconverter. The particulate filter, during operation, can likewise betraversed by the reducing-agent-containing gas flow from the hydrolysiscatalytic converter.

This means that, in operation, the SCR catalytic converter is regularlytraversed by exhaust gas, while this is not normally the case for thehydrolysis catalytic converter and the reducing agent solutionevaporator. The latter are embodied in such a way that they can beconnected to the exhaust line in such a way that a gaseous substancemixture which includes a reducing agent can be introduced into theexhaust line, but at most small quantities of exhaust gas can penetrateinto the hydrolysis catalytic converter and/or the reducing agentsolution evaporator. A reducing agent precursor urea is preferably usedas a precursor for the reducing agent ammonia.

In conventional systems known from the prior art, the hydrolysiscatalytic converter is also traversed by at least a part of the exhaustgas. That requires a hydrolysis catalytic converter of that type tohave, due to the large mass flow rate of the exhaust gas, a certainvolume, often half a liter and more, and a certain surface which is tobe utilized for the catalytic reaction. The volume and the surface canbe considerably smaller in a hydrolysis catalytic converter according tothe present invention, since the hydrolysis catalytic converter needmerely be constructed to be large enough to ensure that it can convertthe maximum required quantity of reducing agent precursor in theevaporated aqueous solution. In this case, the mass flow rates throughthe hydrolysis catalytic converter are considerably lower.

An evaporation of the urea-water solution takes place In the evaporatorunit, during operation. The urea-water solution can contain even furthersubstances which, for example, reduce the freezing point of thesolution. In this case, it is possible for, in particular, formic acidand/or ammonium formate to be contained in the solution. In this case,the evaporator unit is embodied in such a way that, in operation, atleast an evaporation of the urea/water solution takes place. Dependingon the setting of the corresponding temperature and the correspondingquantity of urea/water solution which is supplied to the evaporatorunit, it is also already possible, in addition to the pure evaporationof the urea/water solution, for at least partial thermolysis of the ureato take place to form ammonia. The reducing agent solution evaporator isprovided upstream of the hydrolysis catalytic converter and the latteris provided upstream of the SCR catalytic converter, so that, inoperation, the evaporated aqueous solution which includes a reducingagent precursor and/or a reducing agent, flows from the reducing agentsolution evaporator into the hydrolysis catalytic converter, where atleast a partial hydrolysis takes place to form the reducing agent. Thehydrolysis catalytic converter leaves or yields a gas mixture whichincludes at least reducing agent. The gas mixture is conducted into theSCR catalytic converter and serves there as a selective reducing agentfor reducing nitrogen oxides (NO_(X)).

The internal combustion engine can be mobile or stationary. The internalcombustion engine is, in particular, a part of a land vehicle, watervehicle or aircraft, preferably of an automobile such as, in particular,a passenger or truck or utility vehicle. The hydrolysis catalyticconverter and the SCR catalytic converter denote catalyst carrier bodieswhich are correspondingly catalytically active. The catalyst carrierbodies, in particular, have coatings which are catalytically active orwhich contain catalytically active substances. The catalyst carrierbodies particularly preferably have ceramic coatings, for example in theform of a washcoat in which the correspondingly catalytically activeparticles are distributed. In particular, the hydrolysis catalyticconverter has a coating which includes titanium dioxide (anatase) and/oriron-exchanged zeolites. The SCR catalytic converter particularlypreferably has a coating which includes at least one of the followingcomponents: titanium dioxide, tungsten trioxide, molybdenum trioxide,vanadium pentoxide, silicon dioxide, sulphur trioxide, zeolite.So-called honeycomb bodies, in particular, are used as catalyst carrierbodies. The honeycomb bodies have channels or cavities through which afluid can flow. It is particularly preferable for a honeycomb body to beformed as a catalyst carrier body which is constructed from ceramicand/or metallic material. One option for a honeycomb body is a honeycombbody which is composed of thin sheet metal layers, with at least onestructured and one substantially smooth sheet metal layer being wound orstacked with one another, and at least one of the stacks being coiled.Other catalyst carrier bodies, for example bulk material catalyticconverters, carrier bodies made from wire mesh or the like, are possibleand according to the invention. The construction, in particular, of ahydrolysis catalytic converter in the form of a tube which is providedon the inside with a coating that catalyses the hydrolysis of thereducing agent precursor to form reducing agent, is also preferable. Theprovision of a separate evaporator unit advantageously makes it possibleto continuously ensure a defined dispensing of reducing agent withoutnon-uniform and/or incomplete hydrolysis of the ammonia precursor toform ammonia taking place in the event of increased demand for reducingagent.

According to one advantageous embodiment of the device according to theinvention, the evaporator unit is connected through the use of adelivery line to a reservoir for the aqueous solution, with the deliveryline and the evaporator unit being connected to one another through theuse of a connecting unit.

The connecting unit forms the interface between the delivery line andthe evaporator unit. The connecting unit is constructed so as to ensurea sealed connection between the delivery line and the evaporator unit inorder to avoid leakage of the aqueous solution and of the gaseoussubstance mixture. Furthermore, the connecting unit is constructed insuch a way that, at the same time, a deposition of substances in theinterior of the connecting unit, for example as a result ofprecipitations of components of the corresponding aqueous solution, issuppressed or occurs to such a small extent that a flow through theconnecting unit remains possible. The connecting unit is preferablyconstructed in such a way that it can be cooled. The connecting unit is,for example, connected to a corresponding cooling element. Temperaturecontrol, that is to say cooling or heating, of the connecting unit, isgenerally possible.

According to a further advantageous embodiment of the device accordingto the invention, the connecting unit is formed at least partially froma material with a thermal conductivity of less than 10 W/m K (Watt permeter and Kelvin).

A material with a low thermal conductivity, which is in particular lowerthan that of metals, advantageously permits the formation of aconnecting unit which permits both a high temperature in the evaporatorunit as well as a low temperature in the delivery line to the evaporatorunit. It is possible, in particular, for the delivery line to have atemperature of up to 70° C., up to 80° C. or even up to 90° C. while theevaporator unit has a temperature of more than 300° C., preferably morethan 350° C. and preferably even more than 400° C. A temperature ofapproximately 380° C. is particularly preferable. In this case, the lowthermal conductivity of the material of the connecting unit, inparticular, ensures that no excessive heating of the delivery lineoccurs. Such excessive heating would on one hand lead to heat losses inthe evaporator unit and could on the other hand already cause an atleast partial evaporation of the aqueous solution in the delivery line,which is often undesirable. As a result of the aqueous solution beingpresent in the delivery line, particularly reliable and preciseregulation of the quantity of the aqueous solution supplied to theevaporator unit, and therefore of the quantity of ammonia beingprovided, is possible. In this case, materials are preferable which havea thermal conductivity of only 2 W/m K or less, particularly preferablyonly 1 W/m K or less, in particular between 0.1 W/m K and 0.4 W/m K, inparticular approximately 0.25 W/m K or less. In particular, theconnecting unit is constructed in such a way that its diameter changesby less than 0.25% even if flown through by pulsatile flows. Preferably,the connecting unit is constructed in such a way that the diameterthrough which a fluid can flow is 0.5 to 6 mm in case of a substantiallycircular shape of the region to be flown through. The diameter throughwhich a fluid can flow is preferably 3 to 5 mm, in particularapproximately 4 mm. The region of the connecting unit to be flownthrough preferably has a cross section of 0.2 to 28 square millimetersirrespective of the shape of the region of the connecting unit to beflown through. Preferably, the connecting unit includes at least onePeltier element for cooling and/or heating the connecting unit. Theconnecting unit is, in particular, galvanically isolated from theevaporator unit.

According to a further advantageous embodiment of the device accordingto the invention, the connecting unit is constructed in such a way thata temperature gradient of 40 K/mm (Kelvin per millimeter) and greatercan be maintained over a length of the connecting unit.

This is obtained, in particular, by construction from a correspondingmaterial, by using a coating made from a corresponding material and/orthrough the use of a corresponding topological configuration of theconnecting unit. It is alternatively or additionally possible for theconnecting unit to be equipped with or connected to a correspondingactive or passive temperature control device which allows thetemperature gradient to be maintained.

A temperature gradient of 40 K/mm and greater advantageously permits ahigh temperature of 350° C. or more to be maintained in the evaporatorunit, with a more moderate temperature of, for example, 70° C., 80° C.or 90° C. being maintained in the delivery line. It is thereby possibleon one hand to ensure good and preferably complete evaporation of theaqueous solution with, at the same time, a small spatial extent of theevaporator unit, and a good capability for dosing of the aqueoussolution.

The formation of the connecting unit with a very low thermalconductivity and/or a very large possible temperature gradientadvantageously permits the generation of a very constant temperaturelevel within the evaporator unit without a significantly reducedtemperature in the region adjacent the connecting unit. Such a constanttemperature level of the evaporator unit is advantageous since theformation of depositions or deposits within the evaporator unit can beeffectively avoided or reduced in this way.

According to a further advantageous embodiment of the device accordingto the invention, the connecting unit is constructed from at least onematerial including at least one of the following materials:

-   -   a) a ceramic material, and    -   b) polytetrafluoroethylene (PTFE).

The materials particularly advantageously have, on one hand, a lowthermal conductivity, for example of less than 10 W/m K, and on theother hand advantageously permit the formation of a connecting unit withtemperature gradients of 40 K/mm and greater. It is advantageous, inparticular, when using a ceramic material to use an additional sealingand/or adhesive device in order to increase the impermeability of theconnecting unit.

According to a further advantageous embodiment of the device accordingto the invention, the hydrolysis catalytic converter has a heat capacityof at most 60 J/K.

In this case, the heat capacity of the hydrolysis catalytic converter ispreferably understood to mean the heat capacity without any casing tubewhich may be provided. Such a heat capacity has the effect of permittingthe hydrolysis catalytic converter to be heated and cooled quickly. Thisadvantageously makes it possible to use the hydrolysis catalyticconverter as the regulating element, or one of several regulatingelements, in a temperature regulating circuit. It has additionally beenproven that, in particular when the hydrolysis catalytic converter isnot used in the exhaust gas flow, that is to say in a situation in whichthe hydrolysis catalytic converter is not traversed by exhaust gas ofthe internal combustion engine, an embodiment of the hydrolysiscatalytic converter other than in the exhaust system, where thehydrolysis catalytic converter can also be traversed by exhaust gas, ispossible. A hydrolysis catalytic converter is even preferably formedwith a heat capacity of at most 45 J/K, at most 30 J/K or even of 25 J/Kand less.

The hydrolysis catalytic converter preferably includes a metallichoneycomb body made of a steel having a material code 1.4725 accordingto the German classification of steels and/or aluminum. It is to beunderstood that a steel with material code 1.4725 is, in particular, asteel having 14 to 16 wt.-% (weight-%) chromium, at most 0.08 wt.-%iron, at most 0.6 wt.-% manganese, at most 0.5 wt.-% silicon, 3.5 to 5wt.-% aluminum, at most 0.3 wt.-% zirconium, and a remainder of ironwhich can include usual impurities that add, in particular, up to atmost 0.1 wt.-%. In particular, the steel having a material code 1.4725can be coated and/or bonded with aluminum.

According to a further advantageous embodiment of the device accordingto the invention, the hydrolysis catalytic converter has a volume ofless than 100 ml (milliliters).

Volumes of the hydrolysis catalytic converter of from 5 to 40 ml,preferably of from 10 to 30 ml, have proven to be particularlyadvantageous. These volumes are considerably smaller than the volumes ofhydrolysis catalytic converters which are traversed by exhaust gas. Thevolume of the latter is often 500 ml and greater. The device accordingto the invention is therefore smaller and more cost-effective thansystems known from the prior art.

According to a further advantageous embodiment of the device accordingto the invention, the hydrolysis catalytic converter includes a casingtube.

The casing tube serves to seal off the hydrolysis catalytic converter. Aconstruction of the hydrolysis catalytic converter is preferable inwhich the latter is composed of a catalytically active coating that isapplied to the inner side of the casing tube. It is also advantageousand preferable for the casing tube to serve as a retainer for aconventional structure, for example a honeycomb structure which fills upat least a part of the interior space of the casing tube, or else astructure composed of wire mesh or metal and/or ceramic foam.

According to a further advantageous embodiment of the device accordingto the invention, at least one at least partially structured metalliclayer is provided in the casing tube.

In this case, the hydrolysis catalytic converter can include aconventional honeycomb structure constructed from at least onestructured, in particular corrugated metallic layer and if appropriateat least one further, substantially smooth metallic layer. It isalternatively possible for the hydrolysis catalytic converter to have acasing tube and, on the inner face thereof, to have a structured, inparticular corrugated metallic layer which encircles the entireperiphery of the casing tube at least once, but does not fill up clearor open parts of the cross section of the casing tube, so that a freelytraversable cross section remains free in the interior of the layer.This is referred to as a so-called “hot tube”.

The hydrolysis catalytic converter preferably has channels which aredelimited by walls, with the walls of the channels being at most 80 μm(micrometers) thick. Wall thicknesses of 60 μm and less or 30 μm andless are preferable in this case, in particular where the hydrolysiscatalytic converter is formed at least partially from metallic layerswhich form the walls of the channels. The wall thicknesses have provento be particularly advantageous, since they make it possible to providea hydrolysis catalytic converter with a small heat capacity.

According to a further advantageous embodiment of the device accordingto the invention, the hydrolysis catalytic converter has a cell densityof less than 600 cpsi (cells per square inch).

In relation to conventional hydrolysis catalytic converters which aretraversed by exhaust gas of the internal combustion engine, a hydrolysiscatalytic converter which is not traversed by exhaust gas can beprovided with smaller volumes and smaller surfaces. It is possible, inparticular, in this case for a smaller cell density of the hydrolysiscatalytic converter to be used, since the volume flow rate which flowsthrough the hydrolysis catalytic converter even at full load is lessthan that of exhaust gas. It is thereby possible to use hydrolysiscatalytic converters with relatively low cell densities of less than 600cpsi, of less than 400 cpsi or even of less than 300 or 200 cpsi andless.

According to a further advantageous embodiment of the device accordingto the invention, the hydrolysis catalytic converter is mechanicallyconnected to the exhaust line, in particular flange-connected thereto.This advantageously permits a stable mechanical mounting of the deviceaccording to the invention.

According to a further advantageous embodiment of the device accordingto the invention, the hydrolysis catalytic converter is thermallydecoupled from the exhaust line.

Thermal decoupling is advantageous since, in a cold-start phase of theinternal combustion engine in which the exhaust line is still relativelycool, it is not necessary for the relatively large thermal mass of theexhaust line to also be heated up during the heating of the hydrolysiscatalytic converter. Once the exhaust line has reached its conventionaloperating temperature, which can be up to 800° C. and more and isgreater than the conventional operating temperature of the hydrolysiscatalytic converter of approximately 350 to 450° C., heating of thehydrolysis catalytic converter by the exhaust line which, should itarise, is undesirable and complicates the regulation of the temperatureof the hydrolysis catalytic converter, is prevented.

The operating temperature of the hydrolysis catalytic converter is, inparticular, in the region of 350 to 450° C. whereas the heating of thehydrolysis catalytic converter preferably results from the hot vaporwhich includes reducing agent and/or reducing agent precursor, from afurther electrical heating and/or from waste heat of the evaporator unithaving an operating temperature of up to 450° C. or more.

According to a further advantageous embodiment of the device accordingto the invention, a bar-shaped heating element is provided, through theuse of which at least one of the following components can be heated:

-   -   a) the hydrolysis catalytic converter, and    -   b) at least parts of the evaporator unit.

According to a further advantageous embodiment of the device accordingto the invention, at least one bar-shaped heating element is provided,coaxially with which at least one of the following elements is provided:

-   -   a) the hydrolysis catalytic converter, and    -   b) at least parts of the evaporator unit.

In this embodiment, the hydrolysis catalytic converter can preferably beembodied as an annular honeycomb body which contains a plurality ofchannels between an inner casing tube, which is connected to thebar-shaped heating element, and an outer casing tube. The evaporatorunit can, in particular, contain a metering line which is, inparticular, wound in spiral fashion around the bar-shaped heatingelement. It is, if appropriate, possible for a further heating elementto be provided outside the configuration, so that parts of theevaporator unit and/or of the hydrolysis catalytic converter aresituated between two heating elements. Particularly uniform heating canthereby take place.

The bar-shaped heating element preferably has a plurality of heatingzones with temperatures that can be controlled independently of oneanother. The bar-shaped heating element, in particular, has at least twozones, around which are provided, in each case in one zone, thehydrolysis catalytic converter and the evaporator unit or the meteringline. In particular, the zone of the evaporator unit or of the meteringline is preferably sub-divided further, since different processes takeplace in this case, specifically for example heating of the liquid,evaporation of the liquid and superheating of the liquid. Accordingly, aconfiguration of the bar-shaped heating element with 5 or 6 zones ispreferable. The boundary between the zones can preferably be adapted asa function of the quantity of aqueous solution which is to beevaporated.

According to a further advantageous embodiment of the device accordingto the invention, the temperature of at least one of the followingcomponents can be controlled:

-   -   a) at least parts of the delivery line;    -   b) the hydrolysis catalytic converter;    -   c) at least parts of the evaporator unit;    -   d) a dosing line for metering the generated reducing agent to        the exhaust system; and    -   e) a metering unit, through the use of which the hydrolysis        catalytic converter can be connected to the exhaust line.

In this context, temperature control is to be understood, in particular,to mean that the corresponding component(s) can be heated and/or cooled.In this case, at least one of the components can be part of a regulatingloop, and it is preferable for a plurality of the components to be partsof a regulating loop. It is possible, in particular, for the regulationof the temperature of the components to be carried out in such a waythat one of the components or a plurality of the components are used asa type of actuator. This means, in particular, that the temperature ofonly one of the components is actively controlled, and the componentcorrespondingly sets the temperature of the respective other componentsthrough the use of corresponding reaction kinetics and through the useof the corresponding present fluid-dynamic conditions.

According to a further advantageous embodiment of the device accordingto the invention, a device for temperature control is provided. Thisdevice includes at least one of the following components:

-   -   a) a heating wire;    -   b) a Peltier element;    -   c) a cooling body;    -   d) a bar-shaped heating element;    -   e) a device for burning a fuel; and    -   f) a component made of a material having a positive temperature        coefficient (PTC).

The Peltier element, in particular, can advantageously be used both forheating and for cooling the corresponding component. The cooling bodyadvantageously has a shape which promotes the radiation of heat. Thecooling body is preferably made from a material with high thermalconductivity such as, in particular, aluminum or another metal or ametal alloy.

A Peltier element is to be understood, in particular, as an electricalcomponent which, when a current is passed through it, generates atemperature difference based on the so-called Peltier effect. A Peltierelement preferably includes one or more elements made from p-doped andn-doped semiconductor material which are connected to one anotheralternately through the use of electrically conductive material. Thesign of the temperature difference is dependent on the direction of thecurrent flow, so that both cooling and heating can be provided by aPeltier element.

In this case, a burner is to be understood, in particular, as a devicefor burning a fuel, in particular including hydrocarbons and/orhydrogen. Flameless combustion is also advantageously possible. It is tobe understood that a material having a positive temperature coefficient,a so-called PTC-resistor, is in particular an electroconductive materialhaving an electric resistance which increases with increasingtemperature. These are in use, in particular, as so-calledself-regulating heating elements and are, in particular, made of aceramic material, in particular a barium titanate ceramic.Alternatively, PTC resistors made of a polymeric material being dopedwith soot particles can be used.

According to a further advantageous embodiment of the device accordingto the invention, at least one of the following components has a coatingwhich catalyses the hydrolysis of urea:

-   -   a) at least parts of the connecting unit;    -   b) at least parts of a metering line for metering the gaseous        substance mixture to the hydrolysis catalytic converter;    -   c) at least parts of the evaporator unit;    -   d) at least parts of a dosing line for metering the generated        reducing agent to the exhaust system; and    -   e) at least parts of a metering line, through which the        hydrolysis catalytic converter can be connected to the exhaust        line.

Hydrolysis is advantageously already catalyzed in one of the specifiedcomponents as well as in the hydrolysis catalytic converter, byproviding a coating which catalyses the hydrolysis of urea and which canbe formed, in particular, as specified above. This increases theconversion capacity and makes it possible for the hydrolysis catalyticconverter to be provided to have a correspondingly small volume with asmaller catalytically active surface. The formation of a coating, whichcatalyses the hydrolysis of ammonia, in the dosing line serves, inparticular, to ensure as complete a hydrolysis of ammonia as possible,and in particular also prevents significant proportions of a reversereaction to form urea or another ammonia precursor. A coating whichcatalyses the hydrolysis of urea is to be understood, in particular, tomean that a metering line for metering the aqueous solution to thehydrolysis catalytic converter and/or an evaporator chamber forevaporating the aqueous solution have, at least in parts, a coatingwhich catalyses the hydrolysis of urea. The components can therebyalready cause a partial hydrolysis of the reducing agent precursor toform reducing agent, and thereby improve the effectiveness of thehydrolysis. In addition, the hydrolysis catalytic converter can therebybe fundamentally provided with a smaller volume or with a smallercatalytically active surface than if no corresponding coating wereformed on at least one of the components.

The invention encompasses an embodiment of the device in which theevaporator unit and the hydrolysis catalytic converter cannot betraversed by exhaust gas, but rather only the SCR catalytic convertercan be traversed by exhaust gas. This results in considerably reducedthroughflow rates through the evaporator unit and the hydrolysiscatalytic converter, which can advantageously be incorporated in theconstruction, in particular, of the hydrolysis catalytic converter, sothat the latter can be constructed to be smaller and with a lower celldensity than hydrolysis catalytic converters which are traversed byexhaust gas. This reduces the costs in the production of the deviceaccording to the invention in comparison to devices known from the priorart.

According to a further advantageous embodiment of the device accordingto the invention, a metering unit is provided, through the use of whichthe hydrolysis catalytic converter can be flow-connected to an exhaustline of the internal combustion engine.

Through the use of the metering unit, the reducing agent substancemixture including at least one reducing agent is then metered to theexhaust line. The metering unit can, in particular, include the dosingline, but can also have further components. These can, in particular, bea passive mixing device, through the use of which the introduciblesubstances can be mixed with the exhaust gas.

A passive mixing device is to be understood, in particular, to mean thatno actively moveable mixing device is provided, but that a mixture ofthe substances with the exhaust gas can take place only through the useof the provision of a static mixing device together with thecharacteristics of the exhaust gas flow and the flow of the introduciblesubstances.

It is particularly preferable for the mixing device to include at leastone of the following components:

-   -   a) a guide plate, and    -   b) a honeycomb body which is constructed in such a way that the        exhaust gas can flow through it at least partially at an angle        with respect to the main flow direction of the exhaust gas.

In this case, the guide plate can, in particular, project into theexhaust line. The guide plate can, in particular, be perforated at leastin partial regions and/or have a curvature at least in partial regions.The guide plate can project into the exhaust line at an angle withrespect to the longitudinal direction of the exhaust line at that pointor location.

In particular, the honeycomb body has channels with walls that haveperforations. As a result of the perforations, which can if appropriatebe complemented by correspondingly formed guide structures, flow cantake place at an angle relative to the longitudinal axis of the channel.The honeycomb body can preferably also have a conical construction. Inparticular, the dosing line may open out in the interior of acorresponding cutout of the honeycomb body, so that the correspondingsubstances can be dosed directly in the honeycomb body.

According to a further advantageous embodiment of the device accordingto the invention, the honeycomb body has channels and apertures whichcan be traversed by a fluid and connect adjacent channels to oneanother. The apertures can, in this case, be smaller or larger than theconventional dimensions of a channel.

According to a further advantageous embodiment of the device accordingto the invention, at least one of the following components:

-   -   a) the metering unit, and b) the exhaust line, is constructed in        such a way that, during operation, the opening-out or mouth        region of the metering unit into the exhaust line forms a flow        calming zone or dead zone.

This particularly advantageously has the result that, in operation, thepressure in the exhaust line is lower than in the metering unit or inthe dosing line, so that in this case, substantially no exhaust gasflows in the direction of the hydrolysis catalytic converter. A calmingzone or dead zone is to be understood to mean a region with a lowerpressure than the pressure in the metering unit and/or dosing line. Thiscan be obtained, in particular, in connection with a mixing device whichproduces a calming zone or dead zone directly in the opening-out region,and promotes a mixture downstream of the opening-out region.

According to a further advantageous embodiment of the device accordingto the invention, thermal insulation is provided downstream of thehydrolysis catalytic converter. The thermal insulation is preferablyprovided directly adjoining the hydrolysis catalytic converter.

The thermal insulation prevents thermal contact with the exhaust line,so that on one hand dissipation of heat from the hydrolysis catalyticconverter to the exhaust line and thus cooling down, and on the otherhand dissipation of heat from the exhaust line to the hydrolysiscatalytic converter, can be prevented. In the extreme case, this couldhave the result that thermal regulation can no longer be carried out,since the exhaust line is always also heated as the hydrolysis catalyticconverter is heated.

According to a further advantageous embodiment of the device accordingto the invention, at least one of the following components includes atleast one temperature sensor:

-   -   a) the metering unit;    -   b) the hydrolysis catalytic converter;    -   c) the SCR catalytic converter;    -   d) the evaporator unit;    -   e) the metering line;    -   f) the evaporator chamber; and    -   g) a dosing line for metering the generated reducing agent to        the exhaust line.

The temperature of the corresponding component can be measured by usingthe at least one temperature sensor. The temperature sensor preferablyincludes a thermoresistor. The temperature sensor can preferably beconnected to a power supply. The component can be heated in this way.This can, for example, be necessary in an emergency operating mode ifsubstances have been precipitated in the component and block or threatento block the component. In addition to urea and the like, the substancescan also involve soot which has passed into the metering unit withexhaust gas, for example by diffusion.

According to a further advantageous embodiment of the device accordingto the invention, a delivery device is provided, through the use ofwhich the aqueous solution can be delivered from a reservoir to theevaporator unit. The delivery device preferably includes at least onepump.

As a result of the delivery device, a constant pressure of the aqueoussolution can be built up upstream of the evaporator unit, with dosinginto the evaporator unit taking place through a valve. In anotherpreferred embodiment, the pump is a dosing pump, with the dosing takingplace through the use of a corresponding actuation of the pump. In thiscase, a dosing pump is to be understood as a pump allowing the meteringof a defined volume per time unit or per stroke.

According to a further advantageous embodiment of the device accordingto the invention, the pump can build up a delivery pressure which isgreater than the highest possible exhaust gas pressure on the meteringunit and/or on the dosing line during operation of the internalcombustion engine.

In this way, exhaust gas can be prevented from penetrating into theevaporator unit and/or into the hydrolysis catalytic converter duringoperation. A pump is preferably used which has a delivery rate of up to150 ml/min, preferably of up to 30 ml/min or up to 10 ml/min. A pump ispreferably used having a delivery rate per second which can be varied by0.75 to 2.5 ml/s, in particular which can be increased by these values.

Preferably, a pump is used as a delivery device which can generate ametering pressure of up to 6 bar absolute, preferably up to 2 barabsolute. The volume flow generated by the pump varies with at most 5%around a pretederminable nominal flow. Preferably, the pump is providedin such a way that it is possible to convey back to the reservoir, inparticular with a volume flow which corresponds to the conveying volumeflow.

With the objects of the invention in view, there is also provided amethod for treating exhaust gas of an internal combustion engine. Themethod comprises:

-   -   a) providing a gaseous substance mixture including at least one        of the following substances:    -   b) a1) a reducing agent, or    -   c) a2) at least one reducing agent precursor;

b) hydrolyzing the at least one reducing agent precursor to obtain areducing agent substance mixture;

c) subjecting an SCR catalytic converter to the reducing agent substancemixture and the exhaust gas for at least partial selective catalyticreduction of nitrogen oxides contained in the exhaust gas; and

d) mixing the reducing agent substance mixture with at least parts ofthe exhaust gas after step b).

The method according to the invention can be carried out, in particular,through the use of the device according to the invention. The methodaccording to the invention particularly advantageously permits theprovision of ammonia as a reducing agent for use in the selectivecatalytic reduction of nitrogen oxides, with a highly dynamic method forproviding the ammonia being proposed, so that it is possible to reactquickly to very rapidly rising and therefore highly dynamic demands forammonia as a result of high nitrogen oxide concentrations in the exhaustgas. The mixture of the reducing agent substance mixture with theexhaust gas after step b) means, in particular, that an evaporation ofan aqueous solution including at least one reducing agent precursortakes place outside the exhaust gas flow, and an addition to the exhaustgas of the internal combustion engine takes place only after thehydrolysis of the reducing agent precursor to form the reducing agent. Avariant of the method is preferable in which the reducing agentsubstance mixture is mixed with the entire exhaust gas of the internalcombustion engine. In this case, the reducing agent is preferablyammonia and a reducing agent precursor is preferably urea.

According to an advantageous refinement of the method according to theinvention, step a) includes evaporation, in an evaporator unit, of anaqueous solution including at least one reducing agent precursor.

The reducing agent precursor is preferably urea. In addition to urea,the solution can contain further substances, for example substanceswhich lower the freezing point of the solution. These include, forexample, ammonium formate and/or formic acid. A corresponding solutionis marketed under the trademark “Denoxium”. A further possibility is theuse of a solution which is marketed under the trademark “AdBlue”.

According to a further advantageous embodiment of the method accordingto the invention, step b) at least partially takes place in a hydrolysiscatalytic converter. In this case, the hydrolysis catalytic converterincludes, in particular, a catalyst carrier body which is provided witha coating that catalyses the hydrolysis of ammonia.

According to a further advantageous embodiment of the method accordingto the invention, the temperature of at least one of the followingcomponents is regulated:

-   -   a) at least parts of the evaporator unit;    -   b) the hydrolysis catalytic converter;    -   c) a delivery line for delivering the aqueous solution;    -   d) a metering line for metering the gaseous substance mixture to        the hydrolysis catalytic converter;    -   e) a dosing line for metering the generated reducing agent to        the exhaust system; and    -   f) a metering unit, through the use of which the hydrolysis        catalytic converter can be flow-connected to an exhaust line of        the internal combustion engine.

The regulation of the temperature of at least one of the componentsadvantageously permits precise control of the reaction kinetics withregard to the generated products and the quantity of generated products.It is, for example, possible to meter quantities of ammonia to theexhaust gas which are precisely matched to the present nitrogen oxidecontent in the exhaust gas or to a nitrogen oxide content in the exhaustgas which is forecast for a future time, in order to thereby obtain ascomplete a conversion as possible of the nitrogen oxides in the exhaustgas of the internal combustion engine.

According to a further advantageous embodiment of the method accordingto the invention, the temperature of at least one of the followingcomponents is controlled:

-   -   a) at least parts of the evaporator unit;    -   b) the hydrolysis catalytic converter;    -   c) a delivery line for delivering the aqueous solution to the        evaporator unit;    -   d) a metering line for metering the gaseous substance mixture to        the hydrolysis catalytic converter;    -   e) a dosing line for metering the generated reducing agent to        the exhaust system; and    -   f) a metering unit, through the use of which the hydrolysis        catalytic converter can be flow-connected to an exhaust line of        the internal combustion engine.

As a result of the multiple reaction kinetics processes which take placeduring the reactions according to the invention, it can be sufficient tocontrol the temperature of only parts of one or more of theabove-denoted components or else the overall temperature of one or moreof the above-denoted components. In this case, temperature control is tobe understood, in particular, to mean heating or cooling of thecomponent. It can be sufficient in this case to use one or more of theabove-denoted components as a type of actuator having a temperaturewhich is controlled in such a way that the temperature of the othercomponents is correspondingly changed as a result of the reactionkinetics.

According to a further advantageous embodiment of the method accordingto the invention, the aqueous solution is delivered through a deliveryline to the reducing agent solution evaporator.

The delivery takes place, in particular, through the use of a pump andin particular from a reservoir.

In this context, it is particularly advantageous if the aqueous solutioncan be returned through the delivery line.

This can be advantageous, in particular, when the corresponding systemmust be or is switched off. In an automobile, this can for example bethe case if the driver switches off the ignition of the vehicle. In thiscase, the remaining ammonia present in the dosing line would passunimpeded into the exhaust system and then gradually also into theatmosphere. This is often undesired, and therefore the emissions ofammonia and also of ammonia precursors into the atmosphere can besignificantly reduced and, in particular, prevented through the use of areturn delivery from the delivery line and if appropriate also from themetering line.

According to a further advantageous embodiment of the method accordingto the invention, up to 2.5 ml of aqueous solution are evaporated withinone second.

The evaporator unit is preferably constructed in such a way that up to30 ml/min (milliliters per minute) of the aqueous solution can becontinuously evaporated. With such a method, a dynamic provision ofreducing agent is possible with which it is possible to convert evenconcentration peaks of the concentration of nitrogen oxides.

According to a further advantageous embodiment of the method accordingto the invention, the temperature of at least one of the followingcomponents is determined before the start of a temperature controlmeasure:

-   -   a) the hydrolysis catalytic converter;    -   b) the evaporator unit;    -   c) a dosing line for metering the generated reducing agent to        the exhaust line; and    -   d) a metering unit, through the use of which the hydrolysis        catalytic converter can be connected to the exhaust line,

and is aligned with at least one further temperature of anothercomponent.

The other component is preferably a component which is substantially atthe ambient temperature, for example an external temperature sensor of amotor vehicle, or a cooling water thermometer, etc. In this case, thealignment preferably takes place before the evaporation of the aqueoussolution is initiated. Alignment is to be understood in this case, inparticular, to mean that a comparison of the two temperatures takesplace, with it being possible for further factors to be incorporated.

In this case, it is particularly preferable if an evaporation of theaqueous solution takes place only if the temperature alignment yieldsthat the determined temperature level and the temperature of the othercomponent differ at most by a predefinable difference value.

In predefining the difference value, it is taken into consideration, inparticular, whether or not the system was in operation in a predefinabletimespan and when the system was deactivated. It is also possible topredefine a timespan in which the diagnosis functions do not take placeif the system was in operation within the timespan.

The details and advantages disclosed for the device according to theinvention can also be transferred and applied to the method according tothe invention. The details and advantages disclosed for the methodaccording to the invention can also be transferred and applied to thedevice according to the invention.

Alternatively, the device and the method according to the invention canbe constructed/performed in such a way that a hydrolysis catalyticconverter and a reducing agent solution evaporator conduct a flowthrough them by a partial flow of the exhaust when in use. Alladvantageous improvements disclosed herein in which the hydrolysiscatalytic converter and the reducing agent solution evaporator usuallydo not conduct a flow through them by exhaust when in use can betransferred to an alternative embodiment in which the hydrolysiscatalytic converter and the reducing agent evaporator device conduct aflow through them by a part of the exhaust gas flow when in use.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method and a device for treating the exhaust gas of an internalcombustion engine, it is nevertheless not intended to be limited to thedetails shown, since various modifications and structural changes may bemade therein without departing from the spirit of the invention andwithin the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagrammatic, perspective view of a device for providing agaseous substance mixture in a first embodiment of the invention;

FIG. 2 is an enlarged, longitudinal-sectional view of the firstembodiment of the device for providing a gaseous substance mixture;

FIG. 3 is a fragmentary, longitudinal-sectional view of a delivery linefor delivering an aqueous solution from a reservoir to a metering line;

FIG. 4 is a plan view of a device for the selective catalytic reductionof nitrogen oxide in the exhaust gas of an internal combustion engine;

FIG. 5 is a cross-sectional view of a second exemplary embodiment of anevaporator unit;

FIG. 6 is a fragmentary, cross-sectional view, on a reduced scale, of adevice for providing a reducing agent;

FIG. 7 is a cross-sectional view of an alternative embodiment of theevaporator unit;

FIG. 8 is a fragmentary, perspective view of a portion of an opening-outpoint of a dosing line into an exhaust line;

FIG. 9 is a cross-sectional view of an exemplary embodiment of a devicefor providing a gaseous substance mixture;

FIG. 10 is a block diagram of a device for providing a gaseous substancemixture;

FIG. 11 is a fragmentary, longitudinal-sectional view of an example of apossible metering unit for metering a reducing agent substance mixtureto the exhaust gas;

FIG. 12 is a fragmentary, longitudinal-sectional view of a furtherexample of a possible metering unit for metering the reducing agentsubstance mixture to the exhaust gas;

FIG. 13 is a fragmentary, longitudinal-sectional view of an exemplaryembodiment of a device for treating the exhaust gas of an internalcombustion engine;

FIG. 14 is a perspective view of a device for depositing droplets;

FIGS. 15 to 18 are perspective views of exemplary embodiments ofevaporator units;

FIGS. 19 and 20 are respective perspective and cross-sectional views ofa further exemplary embodiment of a device for providing a gaseoussubstance mixture;

FIG. 21 is a fragmentary, plan view of a further exemplary embodiment ofa device for treating exhaust gas;

FIG. 22 is a fragmentary, plan view of a portion of an opening-outregion of a metering unit into the exhaust line; and

FIGS. 23 and 24 are cross-sectional views of examples of honeycombbodies acting as catalyst carrier bodies.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first,particularly, to FIG. 1 thereof, there is seen a diagrammaticillustration of a device 1 for providing a gaseous substance mixtureincluding at least one of the following substances:

-   -   a) at least one reducing agent, and    -   b) at least one reducing agent precursor.

These are, in particular, the reducing agent ammonia and the reducingagent precursor urea. The device 1 includes a metering line 2 with adispensing opening 3. Furthermore, a device 4 for heating the meteringline 2 is provided. The metering line 2 can be heated with the device 4above a first critical temperature, which is higher than the boilingtemperature of water. The device 1 also includes a reservoir (not shownin FIG. 1) which can be flow-connected to the metering line 2. That isto say, in particular, that a fluid stored in the reservoir, such as forexample an aqueous solution including at least one reducing agentprecursor can, during operation, flow through the metering line 2 to thedispensing opening 3. Through the use of the device 1, a gaseoussubstance mixture can be provided which contains at least one reducingagent and/or at least one reducing agent precursor.

In the present exemplary embodiment, the device 4 for heating themetering line 2 is wound in spiral fashion together with the meteringline 2. In this way, a fluid flowing through the metering line 2 isheated and ultimately evaporated. As a result, a gaseous substancemixture which contains at least one reducing agent precursor isdispensed through the dispensing opening 3. Depending on the selectionof the temperature by using the device 4 for heating the metering line2, at least partial thermolysis of the reducing agent precursor can evenalready take place in the metering line 2, so that the gaseous substancemixture dispensed through the dispensing opening also already containsreducing agent, such as for example ammonia, in addition to a reducingagent precursor, such as for example urea.

Furthermore, the device 1 for providing a gaseous substance mixture alsoincludes a measuring sensor 5, through the use of which the temperatureat least at one point of the metering line 2 can be measured. Themeasuring sensor 5 can, for example, be a conventional thermal elementor a conventional thermoresistor. The device 1 and/or the individualcomponents which require an electrical terminal preferably include acable length for realizing the electrical terminals. A cable length isto be understood, in particular, to mean a cable connection which is atleast half of a meter, preferably at least one meter long. This allowsplug-type contacts to be formed in regions which, in particular inautomobiles, are exposed to only a small extent to environmentalinfluences such as water spray, stone impacts or the like.

FIG. 2 shows the device 1 of FIG. 1 in section. It is possible toclearly see the metering line 2, through which the aqueous solutionincluding at least one reducing agent precursor can flow duringoperation, and the device 4 for heating the metering line 2. Themetering line 2 can have a constant cross section, although it can alsobe variable, as in the present example. In this case, however, thetraversable cross section of the metering line 2 is preferably between0.75 mm² and 20 mm² and the traversable cross section is preferably in aregion of approximately 3 mm². The traversable cross sections have beenproven to be advantageous since, on one hand, fast and substantiallycomplete evaporation of the aqueous solution is possible with a crosssection of that type, and on the other hand, the cross section is largeenough to ensure that the formation of depositions in the interior ofthe metering line 2 is substantially avoided. FIG. 2 also shows themeasuring sensor 5 for determining the temperature of the metering line2.

In this case, the device 4 for heating the metering line 2 is operatedin such a way that, in operation, the temperature across the length ofthe metering line 2 is at most 5° C. above and below a mean temperature.The mean temperature substantially corresponds in this case to the firstcritical temperature. The metering line 2 is formed, in particular, froma copper alloy.

FIG. 3 diagrammatically shows a delivery line 6, through which themetering line 2 can, in operation, be connected to a reservoir (notshown in FIG. 3). The delivery line 6 has a device 7 for temperaturecontrol. In this exemplary embodiment, the device 7 for temperaturecontrol includes in each case a plurality of Peltier elements 8 and acooling body 9. The Peltier elements 8 are in each case provided withelectrical terminals 10, through which they can be supplied withcurrent. In this case, depending on the polarity of the current, thePeltier elements 8 are used for heating or for cooling, so that basictemperature control of the delivery line 6 can be obtained with thePeltier elements 8. The cooling body 9 serves, in particular, to radiateheat energy if the delivery line 6 is cooled by the Peltier element orelements 8.

The delivery line 6 can be connected to a further component through theuse of a connecting unit 11. Depending on the construction of thedevice, the component can be the metering line 2 as already referred toabove, or generally an evaporator unit 12. The metering line 2 can thenbe part of the evaporator unit 12. In general, the connecting unit 11 isformed at least partially from a material with a thermal conductivity ofless than 10 W/m K (Watt per meter and Kelvin). The connecting unit 11is formed, in particular, from a ceramic material and/orpolytetrafluoroethylene (PTFE). The connecting unit 11 is, inparticular, constructed in such a way that a temperature gradient of 40K/mm (Kelvin per millimeter) and greater can be maintained over a length57 of the connecting unit 11. This permits a method to be carried out inwhich the evaporator unit 12 and/or the metering line 2 has aconsiderably higher temperature than the delivery line 6. The evaporatorunit can, for example, have a temperature of 300° C. or more, 400° C. ormore or of 420° C. or more, and thereby lead to substantially completeevaporation of the aqueous solution within the evaporator unit 12, whilethe delivery line 6 has a temperature level of only 70° C. or more, 80°C. or more or 90° C. or more in order to ensure that the aqueoussolution is not yet evaporated in the delivery line 6.

FIG. 4 diagrammatically shows a device 15 for treating exhaust gas 13 ofa non-illustrated internal combustion engine. The exhaust gas 13 of theinternal combustion engine flows through an exhaust line 14. The device15 for treating the gases 13 of an internal combustion engine includes areducing agent solution evaporator 16, a hydrolysis catalytic converter17 and an SCR catalytic converter 18. An aqueous solution including areducing agent precursor is evaporated in the reducing agent solutionevaporator 16. Urea, in particular, is used as a reducing agentprecursor. The reducing agent solution evaporator 16 includes, in thisexemplary embodiment, an evaporator unit 12 including a metering line 2which is heated by a device 4 for heating the metering line 2. Themetering line 2 is connected through a connecting unit 11 to a deliveryline 6. The delivery line 6 is surrounded by a device 7 for controllingthe temperature of the delivery line 6. The device 7 can, for example,include one or more Peltier elements 8 and/or a cooling body 9, as shownabove. The aqueous solution of at least one reducing agent precursor canbe delivered by a delivery device 19 from a corresponding reservoir 20into the delivery line 6. In the evaporator unit 12, a gas is providedwhich includes at least one reducing agent precursor such as, forexample urea, and if appropriate also ammonia which has already beengenerated from the thermolysis of urea. The gaseous substance mixture isintroduced into the hydrolysis catalytic converter 17 provideddownstream of the reducing agent solution evaporator 16. The hydrolysiscatalytic converter 17 is constructed in such a way that, in particular,urea is hydrolyzed to form ammonia through the use of a correspondingcatalytically active coating which is applied to the hydrolysiscatalytic converter 17. In general, the hydrolysis catalytic converter17 serves for the hydrolysis of a reducing agent precursor to form areducing agent. The gas which leaves the hydrolysis catalytic converter17, which gas contains a reducing agent and is referred to as a reducingagent substance mixture, is metered into the exhaust line 14 through adosing line 21. The dosing line 21 opens out into the exhaust line 14 ata dosing opening which is situated upstream of the SCR catalyticconverter 18. A mixing device 23 in the form of a guide plate, which isprovided downstream of the dosing opening 22 and upstream of the SCRcatalytic converter 18, causes a mixture of the reducing agent substancemixture with the exhaust gas 13.

The SCR catalytic converter 18 therefore attains a mixture of reducingagent and exhaust gas which leads to a reduction of the nitrogen oxidescontained in the exhaust gas 13 in the SCR catalytic converter 18. Inthis case, a quantity of reducing agent substance mixture is preferablyprovided which is such that as complete a conversion of the nitrogenoxides in the exhaust gas 13 as possible can take place in the SCRcatalytic converter 18.

FIG. 5 diagrammatically shows a further exemplary embodiment of anevaporator unit 12. This illustration shows the evaporator unit 12 insection. The evaporator unit 12 includes an evaporator chamber 24 whichencompasses a substantially closed volume. In this exemplary embodiment,the evaporator chamber 24 has merely a first opening 25 for connecting adelivery line 6 (not shown in FIG. 5) for delivering the aqueoussolution, and a second opening 26 for connecting a metering line 2 (notshown in FIG. 5) for discharging the gaseous substance mixture. A nozzle62 is provided in the first opening 25 as a device for dosing an aqueoussolution 45 into the evaporator chamber 24. The nozzle 62 serves to dosethe aqueous solution 45 into the evaporator chamber 24. The evaporatorunit 12 additionally has a device for heating the evaporator chamber 24.In the present exemplary embodiment, the device is formed bycorresponding heat conductors 27 which are in contact with theevaporator chamber 24. As is shown in this case, the heat conductors 27can have an asymmetric construction, that is to say a higher density ofheat conductors per unit area is provided in regions which are situatedsubstantially opposite the first opening 25 than in regions which arenot situated substantially opposite the first opening 25. Furthermore,the device cumulatively includes a device 63 for burning hydrocarbons,such as for example a burner. A burner of that type can also be suitablefor carrying out a flameless combustion of hydrocarbons.

The evaporator chamber 24 is preferably formed from a material includingat least one of the following materials: a) copper; b) aluminum; c)noble steel; d) a nickel-based material and e) chrome-nickel steel. Thevolume of the evaporator chamber 24 is preferably 1.5 to 10 cm³. Inoperation, the heat conductor 27 is preferably operated with a heatingpower of up to approximately one kilowatt per second, with the maximumheating power being fixed as a function of the application. In passengervehicles, the maximum heating power is preferably approximately 500 to700 W/s, and in trucks or utility vehicles, preferably approximately1200 to 1500 W/s. The heat capacity of the evaporator chamber 24 ispreferably less than 120 J/K, particularly preferably 100 to 110 J/K.The first opening 25 and the second opening 26 preferably enclose anangle of 30 to 70°. The aqueous solution 45 is preferably delivered atup to 150 ml/min into the evaporator chamber 24, preferably at up to 100ml/min, particularly preferably at up to 30 ml/min. In the region of thesecond opening 26, the evaporator chamber 24 preferably has a devicewith which an infiltration of droplets into the second opening 26 can beavoided. The device is, in particular, a device with which a gas filmsituated between the droplet and the wall of the evaporator chamber 24can be penetrated. The device is, in particular, projections of thewalls or the like. Structures 28 can likewise be provided in thisregion.

Furthermore, the evaporator chamber 24 has, in the interior, one or moreof the above-mentioned structures 28 which serve to produce a largersurface for evaporating the aqueous solution. The structures 28 areillustrated as being relatively large in the present exemplaryembodiment. However, the structures 28 can also be a structured surfacewhich is provided, for example, by applying a corresponding coating tothe inner surface of the evaporator chamber 24. The structures 28 canalternatively or additionally also include macroscopic structures whichhave a structure amplitude of a few millimeters or even more. Ingeneral, the structures 28 are to be understood as a device forincreasing the wetting capacity of the surface of the evaporator chamber24.

FIG. 6 diagrammatically shows the first exemplary embodiment of theevaporator chamber 24 connected to an exhaust line 14. In this case, theevaporator chamber 24 is provided with a casing 29. The casing 29 ispreferably formed from a corresponding thermal insulator which reducesheat losses to the environment. The device 27 for heating the evaporatorchamber 24 can be connected through the use of heat conductor terminals30 to a non-illustrated current source.

The evaporator unit 12 is connected through the use of the secondopening 26 to a hydrolysis catalytic converter 17. The hydrolysiscatalytic converter 17 has a device 31 for controlling the temperatureof the hydrolysis catalytic converter 17. The device 31 is composed, inthe present exemplary embodiment, of a corresponding heating wire whichis wound around the hydrolysis catalytic converter 17. A correspondingcasing 32, which is disposed around the hydrolysis catalytic converter17 constitutes, in particular, thermal insulation of the hydrolysiscatalytic converter 17 with respect to the environment in order tominimize as far as possible any occurring heat losses. In the presentexemplary embodiment, the hydrolysis catalytic converter is connecteddirectly to the exhaust line 14 by virtue of projecting into the latter.A corresponding bore, into which the hydrolysis catalytic converter 17or its casing 32 can be inserted in as sealed a manner as possible, isformed in the exhaust line 14. A corresponding connecting device 33produces as sealed a connection as possible between the hydrolysiscatalytic converter 17 and the exhaust line 14. A passive mixing deviceis also provided in the form of a guide plate 34, through the use ofwhich a reducing agent substance mixture 35, which leaves the hydrolysiscatalytic converter 17, is mixed with the exhaust gas flowing in theexhaust line 14.

In operation, the evaporator unit 12 serves to produce a gaseoussubstance mixture from an aqueous solution which contains urea as areducing agent precursor. The gaseous substance mixture generated in theevaporator unit 12 contains at least urea and if appropriate alsoalready ammonia which has been generated by thermolysis of thecorresponding urea. The substance mixture is conducted through thesecond opening 26 into the hydrolysis catalytic converter 17 in whichsubstantially complete hydrolysis of the urea takes place to formammonia. In this case, a reducing agent substance mixture 35 whichincludes ammonia is generated in the hydrolysis catalytic converter. Amethod is particularly preferred in which 98% and more of the urea isultimately converted to ammonia.

FIG. 7 diagrammatically shows an alternative embodiment of theevaporator unit of FIGS. 5 and 6. In contrast to the first exemplaryembodiment described above, this alternative embodiment additionally hasa third opening 36. In operation, exhaust gas can be introduced into theevaporator chamber 24 in a continuous or pulsatile fashion through thethird opening 36. It is possible in this way to obtain an improveddistribution of the urea in the generated gas in comparison to the firstexemplary embodiment. Furthermore, an evaporator unit 12 of this typecan also be used for evaporating solid urea, since water is introducedinto the evaporator chamber 24 by the exhaust gases of the internalcombustion engine which are introduced through the third opening 36.That water can later be used in the hydrolysis catalytic converter 17for the hydrolysis of the urea to form ammonia.

FIG. 8 diagrammatically shows an opening-out point, mouth or orifice ofa dosing line 21 into the exhaust line 14 as a part of a correspondingmetering unit 46. In this case, the dosing line 21 is surrounded by aheat conductor 38 which is also formed around the opening-out point ofthe dosing line 21 into the exhaust line 14.

FIG. 9 diagrammatically shows, at a first intersection, a furtherpossibility of a device 1 for providing a gaseous substance mixtureincluding a reducing agent. The device 1 includes a metering line 2,around which a corresponding device 4 for heating the metering line 2 iswound, or which is wound together with the device 4. The metering line 2and the device 4 for heating the metering line 2 are formed together ina common casing 29. A first temperature measuring sensor 39 is formedwithin the winding of the metering line 2. The first temperaturemeasuring sensor 39 can be connected through the use of a firstconnecting element 40 to a corresponding control unit (which is notshown in FIG. 9). The evaporator unit 12 is connected at the dispensingopening 3 of the metering line 2 to a hydrolysis catalytic converter 17.The hydrolysis catalytic converter 17 has a coating which catalyses thehydrolysis of urea to form ammonia. The hydrolysis catalytic converter17 is surrounded by a device 31 for controlling the temperature of thehydrolysis catalytic converter. The device 31 includes a correspondinglyformed heating wire. The device 31 for controlling the temperature ofthe hydrolysis catalytic converter 17 can be connected in anelectrically conductive manner to a corresponding power supply throughthe use of corresponding first heat conductor terminals 41. Thiscorrespondingly applies to the device 4 for heating the metering line 2.The device 4 can be provided with a corresponding power supply throughthe use of corresponding second heat conductor terminals 42. Thehydrolysis catalytic converter 17 has a second temperature measuringsensor 43 which can be connected through the use of a correspondingsecond connecting element 44 to a non-illustrated control unit. Thetemperature within or on the hydrolysis catalytic converter 17 can bedetermined through the use of the second temperature measuring sensor43.

In operation, an aqueous urea solution 45 is delivered into the meteringline 2. The device 4 for heating the metering line 2 serves to heat themetering line 2 and thereby evaporate the aqueous urea solution and, ifappropriate, depending on the temperature control, an at least partialthermolysis of the contained urea takes place to form ammonia. Thecorresponding gaseous substance mixture is introduced through thedispensing opening 3 into the hydrolysis catalytic converter 17, inwhich hydrolysis, preferably substantially complete hydrolysis of thecontained urea takes place to form ammonia. A corresponding reducingagent substance mixture 35 leaves the hydrolysis catalytic converter 17.The reducing agent substance mixture 35 can be introduced into anexhaust line 14 of an exhaust system of an internal combustion engine. Amethod is preferable in this case in which the temperatures of theevaporator unit 12 and/or of the hydrolysis catalytic converter 17 aremonitored through the use of the temperature measuring sensors 39, 43,and both components 12, 17 can be heated by the corresponding devices 4,31.

FIG. 10 diagrammatically shows a device 1 for providing a gaseoussubstance mixture 35 including at least one reducing agent. The device 1includes, sequentially, a delivery line 6, through the use of which anaqueous solution is delivered from a non-illustrated reservoir into anevaporator unit 12. The evaporator unit 12 is adjoined by a hydrolysiscatalytic converter 17, and the latter is adjoined by a dosing line 21for metering the corresponding substance mixture to a non-illustratedexhaust line 14 or by a metering unit 46 for metering the reducing agentsubstance mixture to the exhaust line 14. The evaporator unit 12 has athird temperature measuring sensor 47. The temperature of or in thedelivery line 6 can be measured with the third temperature measuringsensor 47. The dosing line 21 and/or the metering unit 46 optionally hasa fourth temperature measuring sensor 48, with which the temperature ofthe dosing line 21 and/or of the metering unit 46 or the temperature inthe dosing line 21 and/or in the metering unit 46 can be measured. Theevaporator unit 12 has a device 4 for heating the metering line 2 and/ora device 27 for heating the evaporator chamber 24. The hydrolysiscatalytic converter 17 can optionally, alternatively or in addition tothe device 4, 27, have a device 31 for controlling the temperature ofthe hydrolysis catalytic converter 17. Optionally, alternatively or inaddition, the delivery line 6 has a temperature control device 49,through the use of which the temperature of the delivery line 6 can becontrolled. It is particularly possible, advantageous and inventive inthis case to use one or more Peltier elements. The dosing line 21 and/orthe metering unit 46 have a metering temperature control device 50,through the use of which the temperature of the dosing line 21 and/or ofthe metering unit 46 can be controlled. The use of at least one Peltierelement is also advantageous in this case. A temperature measuringsensor 43 for the hydrolysis catalytic converter 17 and a temperaturemeasuring sensor 39 for the metering line 2, are also shown.

All of the temperature control devices 4, 27, 31, 49, 50 and all of thetemperature measuring sensors 39, 43, 47, 48 which are provided areconnected to a control unit 51. The control unit 51 carries out aregulation of the temperature in a regulating loop which includes atleast one device 4, 27, 31, 49, 50 for temperature control and at leastone temperature measuring sensor 39, 43, 47, 48. The number oftemperature measuring sensors 39, 43, 47, 48 is preferably greater thanthe number of devices 4, 27, 31, 49, 50 for controlling the temperatureof the components 6, 2, 24, 17, 21, 46. The control unit 51 ispreferably connected to a controller of the internal combustion engineor is integrated therein. The data of the controller of the internalcombustion engine and the operating parameters of the internalcombustion engine can advantageously be incorporated in the control ofthe evaporation and/or of the delivery to the evaporator unit 12.

FIG. 11 diagrammatically shows a portion of a device for providing agaseous substance mixture. A honeycomb body 52 with channels which canbe traversed by a fluid, is provided in an exhaust line 14 upstream ofan SCR catalytic converter 18. The honeycomb body 52 is part of acorresponding mixing device 53. The honeycomb body 52 is constructed insuch a way that it can be traversed by the exhaust gas at leastpartially at an angle with respect to a main flow direction of theexhaust gas. In this case, the main flow direction 54 is indicated by acorresponding arrow in FIG. 11. In the present exemplary embodiment, thehoneycomb body 52 has a conical construction. The honeycomb body has, inparticular, a relatively large cutout 55 which is free from channels.The dosing line 21, as part of the metering unit 46, opens out into thecutout 55. The reducing agent substance mixture 35 is introduced throughthe dosing line 21 in operation.

FIG. 12 diagrammatically shows an example of a metering unit 46 with adosing line 21 for metering the reducing agent substance mixture into anexhaust line 14. In this case, the dosing line 21 extends through thewall of the exhaust line 14 in a curved state. The dosing line 21 hasperforations 56 in a region which projects into the exhaust line 14. Inthis case, the curvature or the curved entry of the dosing line 21 intothe exhaust line 14 is not strictly necessary. The dosing line 21 couldequally well enter into the exhaust line 14 perpendicularly or straight.A guide plate 23, which is additionally provided in this case, leads toa further improved mixture of the reducing agent substance mixture withthe exhaust gas 13 in the exhaust line 14.

FIG. 13 diagrammatically shows an embodiment of the device 1 fortreating the exhaust gas of a non-illustrated internal combustionengine. In this case, the evaporator unit 12 and the hydrolysiscatalytic converter 17 are provided in a first exhaust branch 58. Adistribution of the exhaust gas between the first exhaust gas branch 58and a second exhaust gas branch 59 is obtained by using a device 60 forflow guidance. The SCR catalytic converter 18 is provided downstream ofa mouth or opening-out point 61 of the first exhaust branch 58 into thesecond exhaust branch 59.

The evaporator unit 12 preferably has a device 64 for depositingdroplets. The device 64 can, for example, be provided within themetering line 2 or in or downstream of the second opening 26 of theevaporator chamber 24. FIG. 14 shows an exemplary embodiment of a device64 of that type for depositing droplets. The device 64 is connected tothe metering line 2 or generally to a line 65 through which vaporpasses. Should droplets still be present in the vapor, they aredeposited in the present example by the action of inertia. One or moreimpact plates 66, which force the flow to undergo deflections 67, areprovided in the device 64. The impact plate 66 and/or a housing 68 ofthe device 64 are heated, so that deposited droplets are likewiseevaporated. Instead of the device 64 for depositing droplets which isshown in this case, it is also possible to alternatively or cumulativelytake other measures. For example, the metering line 2 or the line 65 canhave narrowed cross sections, projections, deflections or the like inregions.

FIG. 15 diagrammatically shows a further exemplary embodiment of anevaporator unit 12, in which a metering line 2 can be heated by a device4 for heating the metering line 2. In this case, the device 4 forheating the metering line 2 includes a bar-shaped heating element 69which can be connected through the use of electrical terminals 70 to apower source. A device 64 for depositing droplets, which is provided inthe metering line 2, can be heated due to contact with the rod-shapedheating element 69.

FIG. 16 diagrammatically shows a further exemplary embodiment of anevaporator unit 12 in which the metering line 2 is wound, in the form ofa loop, twice around the bar-shaped heating element 69.

FIGS. 17 and 18 show exemplary embodiments of evaporator units 12 inwhich the metering line 2 is not wound around the longitudinal axis ofthe bar-shaped heating element 69 but is fastened in loops to thebar-shaped heating element 69. A materially-joined connection betweenthe metering line 2 and the bar-shaped heating element 69, in particulara brazed connection, is fundamentally preferred.

FIGS. 19 and 20 diagrammatically show a further exemplary embodiment ofa device 1 for providing a gaseous substance mixture including at leastone of the following substances: a) a reducing agent, preferablyammonia, and b) at least one reducing agent precursor, in particularurea, having a hydrolysis catalytic converter 17. The device 1 includesat least one metering line 2, in the present exemplary embodiment fourmetering lines 2, which are wound in spiral fashion around a bar-shapedheating element 69. Each of the metering lines 2 has a respectivedispensing opening 3, through which, in operation, a gaseous substancemixture which includes a reducing agent, is dispensed. The respectivedispensing openings 3 are distributed, so as to be distributedsubstantially uniformly on a circle. The metering lines 2 are connectedto a non-illustrated reservoir 20 from which an aqueous solution 45 ofat least one reducing agent precursor is delivered into the meteringline 2 by a delivery device 19. The metering lines 2 and the heatingelement 69 are part of a corresponding reducing agent solutionevaporator 16.

The hydrolysis catalytic converter 17, which is disposed downstream ofthe dispensing openings 3, can likewise be heated by a bar-shapedheating element 69. In one advantageous refinement, only one bar-shapedheating element 69 is provided. The heating element 69 is in thermalcontact both with the metering line or lines 2 and with the hydrolysiscatalytic converter 17. In the present exemplary embodiment, thehydrolysis catalytic converter 17 is embodied as an annular honeycombbody. The hydrolysis catalytic converter 17 is adjoined downstream by adosing line 21, through which, in operation, the gas flow including atleast one reducing agent can be introduced into the exhaust line 14. Amechanical connection to the exhaust line 14 can be produced by aconnecting device 71. A thermal insulation 72 is also provided, throughwhich the hydrolysis catalytic converter 17 is thermally decoupled fromthe exhaust line 14. A heat shield 73 is also provided, through whichthe hydrolysis catalytic converter 17 is protected from a radiation ofheat. Furthermore, air gap insulation 74, which likewise serves asthermal insulation, is provided between an outer housing 75 and an innerhousing 76.

FIG. 20 shows a cross section through that region of the metering lines2 which can be seen encircling the rod-shaped heating element 69.

FIG. 21 diagrammatically shows a further exemplary embodiment of adevice 15 for treating exhaust gas 13. In contrast to the embodiment inFIG. 4, a valve 77 is provided in the delivery line 6. The valve 77serves for dosing the aqueous solution 45 into the evaporator unit 12.The valve 77 can be actuated through the use of a control terminal 78.

FIG. 22 diagrammatically shows an opening-out or mouth region 79 of ametering unit 46 into the exhaust line 14. In this case, the exhaustline 14 and/or the metering unit has a shield or screen 80 which, inoperation, produces a dead zone or calming zone of the exhaust gas flow,and consequently a region of reduced pressure, in the opening-out region79, and thereby ensures that no exhaust gas is pushed into the dosingunit 46. The metering or dosing unit 46 also has a temperature sensor 81which includes an annular thermoresistor. Should depositions form in theregion, then the temperature sensor 81 can be connected to anon-illustrated power source in order to thereby bring about atemperature increase to a second nominal temperature, for example of550° C. or more or even of 600° C. and more, and cause a dissolution orreduction of the depositions.

FIG. 23 diagrammatically shows a cross section through a honeycomb body82 which can be used both as a hydrolysis catalytic converter 17 andalso as an SCR catalytic converter 18, noting that it is necessary inthis case for other catalytically active coatings to be applied. Thehoneycomb body 82 is constructed from smooth metallic layers or sheets83 and corrugated metallic layers or sheets 84 which, in this exemplaryembodiment, are layered to form three stacks and are then wound with oneanother. The honeycomb body 82 also includes a casing tube 85 whichcloses off the honeycomb body 82 from the outside. The smooth layers 83and corrugated layers 84 form channels 86 through which the exhaust gas13 can flow.

FIG. 24 shows a further example of a honeycomb body 87 which has anannular construction and can be used both as a hydrolysis catalyticconverter 17 and also as an SCR catalytic converter 18, noting that itis necessary in this case for other catalytically active coatings to beapplied. The honeycomb body 87 is constructed from layers 88 which havesmooth sections 89 and corrugated sections 90 that are folded onto oneanother and form channels 86 through which the exhaust gas 13 can flow.The honeycomb body 87 is closed off through the use of an outer casingtube 91 and an inner casing tube 92.

In the case, in particular, of a metering line 2 which is heated by adevice 4, 69, it is fundamentally advantageous to provide heating fromthe other side, in addition to single-sided heating. It is, for example,possible for further heating elements to be provided which enclose themetering line from the outside. It is fundamentally advantageous if, ata certain cross section of the metering line 2, the temperature over theperiphery differs from a mean temperature at most by +25° C. or −25° C.in operation.

The hydrolysis catalytic converter 17 is fundamentally also a tube whichis provided with a coating that catalyses the hydrolysis, in particular,of urea to form ammonia, or else a casing tube having at least onestructured metallic layer which is applied on the inside to the outerperiphery and which preferably has a freely traversable cross sectionradially in its interior which is at least 20% of the entire crosssection of the casing tube. These embodiments are preferably heated fromthe outside.

Before the provision of a reducing agent upstream of the SCR catalyticconverter 18 commences, the process is fundamentally as follows:

-   -   it is initially checked as to whether a current supply or fuel        supply is ensured for the temperature control and/or heating        device 4, 27, 31, 49, 50, 63, 69;    -   if it is determined that the current and/or fuel supply is        ensured, then the evaporator unit 12 and if appropriate the        hydrolysis catalytic converter 17 are heated in each case to a        predetermined nominal temperature, in particular a metering line        2 is heated to approximately 350 to 450° C. and/or an evaporator        chamber 24 is heated to approximately 350 to 450° C., preferably        in each case approximately 380° C.; an aqueous solution 45 is        delivered in parallel to the evaporator chamber 24, in        particular to the connecting unit 11, with it being possible on        one hand for a volume of aqueous solution 45 to be delivered        which substantially corresponds to the volume of the delivery        line 6, and on the other hand for a corresponding sensor, which        operates for example on the basis of conductivity measurement,        to be provided at a corresponding point, for example on, in or        adjacent the connecting unit 11;    -   the temperature of the SCR catalytic converter 18 or of the        exhaust line 14 is then determined, in particular measured        and/or calculated from the data of an engine controller.

If the temperature of the SCR catalytic converter 18 is above apredefinable limit value, in particular the “light-off” temperature ofthe SCR catalytic converter 18, the evaporator unit 12 is supplied withthe aqueous solution 45. If the evaporator unit 12, the metering line 2and/or the evaporator chamber 24 are still substantially at theiroperating temperature, then the above-specified diagnosis steps can beomitted.

In operation, the heating power imparted to the evaporator unit 12correlates with the delivery quantity of the aqueous solution 45. Thismeans, in particular, that it is checked as to what level of nominalheating power is required for the evaporation of the respective deliveryquantity. If the measured actual heating power for a timespan is belowthe nominal heating power, then a warning is output to the user, since areduction of the cross section of the metering line 2 and/or of thedosing line 21 could then be present.

It is also advantageous, at regular, predefinable time intervals, toheat the evaporator unit 12, the metering line 2, the evaporator chamber24, the hydrolysis catalytic converter 17, the dosing line 21 and/or themetering unit 46 to a temperature which is above the normal operatingtemperature, in order to thereby dissolve any depositions which may bepresent.

When the evaporation is ended, which occurs for example when theinternal combustion engine is switched off, the aqueous solution 45 canbe returned from the metering line 2. Before the return delivery fromthe metering line 2, the delivery of aqueous solution 45 is preferablyfirstly suspended, with the evaporator unit 12, the metering line 2and/or the evaporator chamber 24 however still being heated to the usualtemperature in order to thereby carry out complete evaporation and tothereby prevent any impurities present in the evaporator unit 12, themetering line 2 and/or the evaporator chamber 24 from passing into thedelivery line 6 during the return delivery. After a certain time haselapsed, the return delivery can be initiated by the delivery device. Avalve is advantageously provided on or adjacent the connecting unit 11.Air can be sucked in during the return delivery through the use of thevalve. The return delivery fundamentally takes place until the deliveryline 6 is substantially emptied into the reservoir 20.

In the event of intense changes in the delivery quantity of the aqueoussolution 45 which is to be delivered, which can for example beattributed to a sharply-rising concentration of nitrogen oxides in theexhaust gas of the internal combustion engine, situations can occur inwhich the evaporator unit 12 is not capable of immediately evaporating aconsiderably higher quantity of aqueous solution 45, since thecorrespondingly increased heating cannot take place so quickly. In thiscase, it is preferable to increase the delivery quantity of the aqueoussolution 45 only to such an extent that complete evaporation is stillpossible.

The quantity of reducing agent to be dispensed, and consequently alsothe quantity of aqueous solution 45 which is to be evaporated, can bedetermined as a function for example, of at least one of the followingconditions:

-   -   a) the nitrogen oxide concentration in the exhaust gas;    -   b) a forecast nitrogen oxide generation which preferably occurs        when the exhaust gas passes the SCR catalytic converter 18;    -   c) the maximum quantity of reducing agent which can be converted        directly by the SCR catalytic converter 18.

The reservoir 20, the delivery line 6, the evaporator unit 12, themetering line 2, the evaporator chamber 24 and/or the hydrolysiscatalytic converter 17 can be constructed to be in thermal contact, forexample with the fuel tank of the internal combustion engine. The fueltank usually has a heater, for frost protection reasons, which can thenalso provide frost protection for the above-specified components.

According to a further advantageous aspect, a device 1 is proposed forproviding a gaseous substance mixture including at least one of thefollowing substances:

-   -   a) at least one reducing agent, and    -   b) at least one reducing agent precursor.

In this case, the device 1 includes a reservoir 20 for an aqueoussolution 45 including at least one reducing agent precursor. The aqueoussolution 45 can be delivered from the reservoir 20 into at least onemetering line 2 with a dispensing opening 3 by a delivery device 19.Advantageously, through the use of the device 4 for heating the meteringline 2, the at least one metering line 2 can be heated above a criticaltemperature which is greater than the boiling temperature of water. Thetemperature is preferably 350° C. or more, preferably 400° C. or more,in particular approximately 380° C. One advantageous refinement of thedevice 1 provides that the delivery device 19 includes at least onepump. The latter is preferably a dosing pump. According to a furtheradvantageous refinement of this device, a valve for dosing the quantityof aqueous solution 45 is provided between the delivery device 19 andthe metering line 2. The device 4 for heating also advantageouslyincludes at least one of the following elements:

-   -   a) an electrical resistance heater;    -   b) a heat transfer device for utilizing the waste heat of at        least one other component;    -   c) at least one Peltier element; and    -   d) a device for burning a fuel.

A further advantageous embodiment of the device is distinguished in thatthe device 1 is constructed in such a way that, in operation, thetemperature across the length of the metering line 2 is at most 25° C.above and below a mean temperature.

A further advantageous embodiment of the device is distinguished in thatthe metering line 2 has a traversable cross section of at most 20 mm².It is also advantageous if the metering line 2 is formed from a materialincluding at least one of the following materials:

-   -   a) copper;    -   b) aluminum;    -   c) a nickel-based material;    -   d) chrome-nickel steel; and    -   e) noble steel.

The metering line 2 has, in particular, a length of from 0.1 to 5 m,preferably a length of from 0.3 to 0.7 m, particularly preferablysubstantially 0.5 m. The metering line 2 preferably has a wall thicknessof 0.1 to 0.5 mm. The metering line 2 preferably has a heat capacity ofat least 150 J/K (Joule per Kelvin).

According to a further advantageous embodiment of the device 1, themetering line 2 and the device 4 for heating the metering line 2 have,at least in at least one partial region, at least one of the followingconfigurations relative to one another:

-   -   a) the metering line 2 and the device 4 for heating the metering        line 2 are formed coaxially with respect to one another at least        in a partial region;    -   b) the metering line 2 and the device 4 for heating the metering        line 2 are provided concentrically with respect to one another        at least in a partial region;    -   c) the metering line 2 and the device 4 for heating the metering        line 2 are provided adjacent one another at least in a partial        region;    -   d) the metering line 2 is provided at least in a partial region        so as to be wound around the device 4 for heating the metering        line 2;    -   e) the device 4 for heating the metering line 2 constitutes, at        least in partial regions, a bar-shaped heating element 69, with        the metering line 2 being formed so as to be wound around the        bar-shaped heating element 69; and    -   f) the metering line 2 forms a channel or duct in a bar-shaped        heating element 69.

According to a further advantageous embodiment of the device 1, themetering line 2 and the device 4 for heating the metering line 2 areconnected to one another in a materially joined fashion at least inpartial regions. A materially joined connection is to be understood, inparticular as a soldered, brazed and/or welded connection.

According to a further advantageous embodiment of the device 1, themetering line 2 is at least partially provided with a coating whichcatalyses the hydrolysis of a reducing agent precursor to form areducing agent. The device 1 preferably includes at least one measuringsensor 5 for determining the temperature of the metering line 2. Themeasuring sensor can preferably be connected to a power source 5 inorder to thereby permit, for example within the context of an emergencyprogram, heating of the metering line 2 above the critical temperature.

An advantageous method is also described for providing a gaseoussubstance mixture including at least one of the following substances:

-   -   a) at least one reducing agent, and    -   b) at least one reducing agent precursor.

In this case, an aqueous solution 45 of at least one reducing agentprecursor is delivered from a reservoir 20 into a metering line 2. Inthis case, the metering line 2 is heated in such a way that the aqueoussolution 45 is completely evaporated to form the gaseous substancemixture. Completely is to be understood herein, in particular, to meanan evaporation in which 90% by weight and more of the aqueous solution,preferably 95% by weight and more, particularly preferably 98% by weightof the aqueous solution, is evaporated. One advantageous refinement ofthe method is aimed at least at one of the reducing agent precursors:

-   -   a) urea, and    -   b) ammonium formate,

being included in at least one of the following components:

-   -   A) the substance mixture, and    -   B) the aqueous solution.

It is also advantageous for the temperatures in the metering line 2 tobe at a mean temperature between 380° C. and 450° C. The temperaturealong a length of the metering line 2 is preferably at most 25° C. aboveor below a mean temperature, preferably a mean temperature of 380° C. to450° C.

According to a further advantageous embodiment of the method, a heatingpower which varies by up to 500 W/s is used during the heating process.A quantity of 0.5 ml/s of the aqueous solution 45 is preferablydelivered into the metering line 2. It is also preferable for themetering line 2 to have a traversable cross section of at most 20 mm².The metering line 2 is preferably heated to a second temperature whichis higher than the critical temperature at which complete evaporation ofthe aqueous solution 45 takes place, in order to thereby dissolve, ifappropriate, any depositions which may be present.

According to a further advantageous embodiment of the method, thetemperature of the metering line 2 is determined before the start of theevaporation, and is aligned with other known temperatures. In this casethese can, for example, be other known or measured temperatures in theautomobile, such as for example the ambient temperature measured throughthe use of an external temperature sensor, or the cooling watertemperature.

According to a further advantageous embodiment of the method, theheating of the metering line 2 is carried out through the use of anelectrical resistance heater, with the resistance of the resistanceheater being determined before the start of heating and the heating ofthe metering line taking place as a function of the determinedresistance. A further advantageous refinement of the method is aimed atthe introduced heating power during the heating of the metering line 2being monitored. According to a further advantageous embodiment of themethod, the heating is interrupted if, over a predefinable timespan, theheating power remains below a value which is dependent on the quantityof aqueous solution to be evaporated.

According to a further advantageous present aspect, a device 1 isdescribed for providing a gaseous substance mixture including at leastone of the following substances:

-   -   a) at least one reducing agent, and    -   b) at least one reducing agent precursor.

In this case, a reservoir 20 for an aqueous solution 45 including atleast one reducing agent precursor, is provided. The reservoir 20 can beflow-connected to an evaporator chamber 24. Furthermore, a device fordosing the aqueous solution 45 is provided in the evaporator chamber 24.The device 27, 63 for heating the evaporator chamber 24 is provided forheating the evaporator chamber 24 to a temperature greater than or equalto a critical temperature at which the aqueous solution is at leastpartially evaporated. According to one advantageous refinement of thedevice 1, the device for dosing the aqueous solution 45 includes atleast one nozzle 62. The evaporator chamber 24 advantageously has asubstantially closed volume which has only a first opening 25 forconnecting a delivery line 6 for the aqueous solution 45, and a secondopening 26 for connecting a metering line 2 for discharging the gaseoussubstance mixture. According to one advantageous refinement of thedevice 1, the evaporator chamber 24 encompasses a substantially closedvolume which has only a first opening 25 for connecting a delivery line6 for the aqueous solution, a second opening 26 for connecting ametering line 2 for discharging the gaseous substance mixture, and athird opening 36 for metering exhaust gas 13. A further advantageousrefinement of the device provides that the device 27, 63 for heating theevaporator chamber 24 includes at least one of the following components:

-   -   a) an electrical resistance heater 27, and    -   b) a device 63 for burning a fuel.

It is also advantageous that the evaporator chamber 24 is substantiallyspherically symmetrical. In this case, the evaporator chamber 24preferably has a radius of 2 mm to 25 mm. It is also advantageous forthe evaporator chamber 24 to have a volume of 30 to 4,000 mm³. Thedevice 27, 63 for heating the evaporator chamber can impart a heatingpower of up to 5 kW. A delivery line 6 for delivering the aqueoussolution 45 is also advantageously provided. The delivery line 6connects the evaporator chamber 24 to a reservoir 20 and a deliverydevice 19 is provided therein, through the use of which a fluid can bedelivered through the delivery line 6. According to a furtheradvantageous embodiment of the device, the latter is constructed in sucha way that, during operation, the temperature of the evaporator chamber24 is at most 25° C. above and below a mean temperature. It is alsoadvantageous for the evaporator chamber 24 to have, at least in partialregions, a device 28 for increasing the wetting capacity of the surface.The device 28 can, in particular, include a structuring of the innersurface (projections or the like) of the evaporator chamber 24.

A method is also described for providing a gaseous substance mixtureincluding at least one of the following substances:

-   -   a) at least one reducing agent, and    -   b) at least one reducing agent precursor.

An aqueous solution 45 of at least one reducing agent precursor isdelivered into an evaporator chamber 24, with the evaporator chamber 24being heated in such a way that the aqueous solution 45 is completelyevaporated to form the gaseous substance mixture. The method canadvantageously be further developed in such a way that the evaporatorchamber 24 includes a substantially closed volume which has only a firstopening 25 for connecting a delivery line 6 for the aqueous solution 45,and a second opening 26 for connecting a metering line 2 for dischargingthe gaseous substance mixture.

Alternatively, the evaporator chamber 24 can encompass a substantiallyclosed volume which has only a first opening 25 for connecting adelivery line 6 for the aqueous solution 45, a second opening 26 forconnecting a metering line 2 for discharging the gaseous substancemixture, and a third opening 36 for metering exhaust gas 13.

The methods can advantageously be further developed in such a way thatthe heating is regulated. The evaporator chamber 24 is, in particular,heated to a mean temperature of 350 to 450° C. It is also advantageousfor the evaporator chamber 24 to be heated to a mean temperature in sucha way that the temperature does not at any point or location of theevaporator chamber 24 deviate from a mean temperature by more than +25°C. or −25° C.

The device 15 according to the invention advantageously permits theprovision of a sufficiently large quantity of reducing agent for theselective catalytic reduction of nitrogen oxides in the SCR catalyticconverter 18, with it being possible at the same time for the hydrolysiscatalytic converter 17 to be constructed with a smaller volume than isknown from the prior art, since the hydrolysis catalytic converter 17 inthis case is not traversed by exhaust gas.

1. A device for treating exhaust gas of an internal combustion enginepassing through an exhaust line, the device comprising: a reducing agentsolution evaporator disposed outside the exhaust line and to beconnected to the exhaust line, said reducing agent solution evaporatorincluding an evaporator unit configured for evaporating an aqueoussolution including at least one reducing agent precursor and forproviding a gaseous substance mixture including at least one of thefollowing substances: a) at least one reducing agent precursor, or b) areducing agent; a hydrolysis catalytic converter connected to saidreducing agent solution evaporator, disposed outside the exhaust lineand to be connected to the exhaust line; and an SCR catalytic converterdisposed in the exhaust line for selective catalytic reduction ofnitrogen oxides.
 2. The device according to claim 1, wherein saidhydrolysis catalytic converter is configured for hydrolysis of urea toform ammonia.
 3. The device according to claim 1, which furthercomprises a reservoir for the aqueous solution, a delivery lineconnected to said reservoir, and a connecting unit connected betweensaid delivery line and said evaporator unit.
 4. The device according toclaim 3, wherein said connecting unit is formed at least in part of amaterial having a thermal conductivity of less than 10 W/m K (Watts perMeter and Kelvin).
 5. The device according to claim 3, wherein saidconnecting unit is formed of at least one substance including at leastone of the following materials: a) a ceramic substance, or b)polytetrafluoroethylene (PTFE).
 6. The device according to claim 3,wherein said connecting unit has a length and is configured formaintaining a temperature gradient of 40 K/mm (Kelvin per millimeter)and greater over said length.
 7. The device according to claim 3, whichfurther comprises: a metering line for metering the gaseous substancemixture to said hydrolysis catalytic converter; a dosing line formetering a generated reducing agent to the exhaust line; a metering unitfor connecting said hydrolysis catalytic converter to the exhaust line;and a coating catalyzing the hydrolysis of urea, said coating disposedon at least one of: a) at least parts of said connecting unit; b) atleast parts of said metering line; c) at least parts of said evaporatorunit; d) at least parts of said dosing line; or e) at least parts ofsaid metering unit.
 8. The device according to claim 1, which furthercomprises thermal insulation disposed downstream of said hydrolysiscatalytic converter.
 9. The device according to claim 8, wherein saidthermal insulation directly adjoins said hydrolysis catalytic converter.10. A method for treating exhaust gas of an internal combustion engine,the method comprising the following steps: a) providing a gaseoussubstance mixture including at least one of the following substances:a1) a reducing agent, or a2) at least one reducing agent precursor; b)hydrolyzing the at least one reducing agent precursor to obtain areducing agent substance mixture; c) subjecting an SCR catalyticconverter to the reducing agent substance mixture and the exhaust gasfor at least partial selective catalytic reduction of nitrogen oxidescontained in the exhaust gas; and d) mixing the reducing agent substancemixture with at least parts of the exhaust gas after step b).
 11. Themethod according to claim 10, which further comprises carrying out stepa) by evaporation of an aqueous solution including at least one reducingagent precursor, in an evaporator unit.
 12. The method according toclaim 11, which further comprises at least partially carrying out stepb) in a hydrolysis catalytic converter.
 13. The method according toclaim 12, which further comprises: delivering the aqueous solutionthrough a delivery line to the evaporator unit; metering the gaseoussubstance mixture to the hydrolysis catalytic converter with a meteringline; metering a generated reducing agent to an exhaust line of theinternal combustion engine with a dosing line; flow-connecting thehydrolysis catalytic converter to the exhaust line with a metering unit;and regulating a temperature of at least one of: a) at least parts ofthe evaporator unit; b) the hydrolysis catalytic converter; c) thedelivery line; d) the metering line; e) the dosing line; or f) themetering unit.